// 设置画布

const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');

const width = canvas.width = window.innerWidth;
const height = canvas.height = window.innerHeight;

// 生成随机数的函数

function random(min,max) {
  const num = Math.floor(Math.random() * (max - min)) + min;
  return num;
}

//生成随机颜色值的函数
function randomColor() {
  const color = 'rgb(' +
                random(0, 255) + ',' +
                random(0, 255) + ',' +
                random(0, 255) + ')';
  return color;
}

// 定义 Ball 构造器
function Ball(x, y, velX, velY, color, size) {
  this.x = x; //小球的水平坐标
  this.y = y; //小球的垂直坐标
  this.velX = velX; //水平速度
  this.velY = velY; //垂直速度
  this.color = color; //小球颜色
  this.size = size; //小球半径
}

// 定义彩球绘制函数
Ball.prototype.draw = function() {
  ctx.beginPath(); //声明开始绘制
  ctx.fillStyle = this.color; //填充颜色
  ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI); //绘制圆形
  ctx.fill(); //填充
}

// 定义彩球更新函数
Ball.prototype.update = function() {
  if((this.x + this.size >= width)) {
    this.velX = -(this.velX);
  }
  if((this.x - this.size <= 0)) {
    this.velX = -(this.velX);
  }
  if((this.y + this.size >= height)) {
    this.velY = -(this.velY);
  }
  if((this.y - this.size <= 0)) {
    this.velY = -(this.velY);
  }
  this.x += this.velX; //更新水平坐标
  this.y += this.velY; //更新垂直坐标
}

// 定义碰撞检测函数
Ball.prototype.collisonDetect = function() {
  for(let j = 0; j < balls.length; j++)  {
    if(this != balls[j]) {
      const dx = this.x - balls[j].x;
      const dy = this.y - balls[j].y;
      const distance = Math.sqrt(dx * dx + dy * dy);
      if(distance < this.size + balls[j].size) {
        balls[j].color = this.color = randomColor();
      }
    }
  }
}

//定义一个数组来保存所有的球
let balls = [];

while (balls.length < 25) {
  const size = random(10, 20);
  let ball = new Ball(
    random(0 + size, width - size), //x坐标
    random(0 + size, height - size), //y坐标
    random(-7, 7), //水平速度
    random(-7, 7), //垂直速度
    randomColor(), //颜色
    size //半径
  );
  balls.push(ball);
}

//定义一个循环来不停地播放
function loop() {
  ctx.fillStyle = 'rgba(0, 0, 0, 0.25)'; //半透明黑色
  ctx.fillRect(0, 0, width, height); //绘制一个填充满整个画布的矩形

  for(let i = 0; i < balls.length; i++) {
    balls[i].draw(); //绘制球
    balls[i].update(); //更新球的数据
    balls[i].collisonDetect(); //检测碰撞
  }

  requestAnimationFrame(loop); //递归调用函数
}

loop(); //调用函数